In recent years, light emitting diodes have been used as an alternative to the conventional light sources in a variety of fields due to their thrifty power consumption. Ultraviolet light-LEDs (hereafter, UV-LEDs) have been also proposed for use as a light source curing photo-curable resins (the patent document 1: JP-A-2008-163,183). UV-LEDs generally have single-peaked wavelength distribution. Use of the UV-LED having its peak at, for example, 360 nm to 370 nm is expected to decrease ultraviolet light damage caused by mainly short-wavelength, and together to increase production efficiency.
However, UV-LED is deficient in the light with short-wavelength (for example, a range not longer than 300 nm, yet even not longer than 350 nm) required to reduce oxygen inhibition and to achieve acceptable surface curing. Consequently, curing by means of UV-LED as a light source presents a problem with defective curing of resin surface due to oxygen inhibition.
List of Documents                Patent document 1: JP-A-2008-163,183        Patent document 2: JP-A-H1-22,927 (JP-B-H6-60,238)        